Vacuum-responsive glow-tube control for rectifiers



L. SMEDE VACUUI RESPONSIVE GLOW TUBE CONTROL FOR RECTIFIERS Filed Augr.6, 1927 ATTORNEY Patented June 4,1929,

UN1TED STATES 1,716,155 PATENT OFFICE.

TBIC MANUFACTURING COMPANY,

A CORPORATION 0F PENNSYLVANIA.

VACUUM-RESPONSIVE GLOW-TUBE CONTROL FOB RECTIFIERS.

Application led `August: 6, 1927. Serial No. 211,104.

My invention relates to vacuum-responsive devices, and it has particularrelation to means for obtaining an indication of an increase in gaspressure in an evacuated vessel.

The principal object of my invention is to provide means utilizing aglow-discharge dcvice which is responsive to the vacuum in question andwhich breaks down upon the attainment of a predetermined gaseouspressure, as a means for obtaining an automatic response to a change inthe degree of vacuum existing in an evacuated vessel.

A further object of my invention is to provide an auxiliary means,associated with the means just mentioned, for the purpose of operatingin response to still further increases in the gas pressure and beforethe glow-discharge device ceases to discharge as a result of saidincreased gas pressure.

With the foregoing and other objects in view, which will be readilyunderstood from the following description and claims, my inventionconsists of the lovel features and' combinations hereinafter describedand claimed and illustrated in the accompanying drawing, wherein Figure1 is a diagrammatic view of circuits and apparatus embodying myinvention in a preferred form, some parts of the device being indicatedin section and other parts being indicated diagrammaticall Fig. 2 is acurve diagram which will be subsequently referred to;

Fig. 3 is a bottom plan view of the central portion of the bottomelectrode of my improved glowedischarge device; and

Fig. 4 is a cross-sectional view of a differentform of glow-dischargedevice.

My invent-ion is particularly adapted to the automatic control of ametaLtank mercury-arc rectifier. which is indicated at 4 on the drawing.The rectifier is supplied with energy, in the usual way, from thesecondary member of a main transformer 6 which is energized through ahigh-tension oil switch 8. The oil switch is provided with closing andopening coils 9 and 10, respectively. The rectifier tank is eithercontinuously or intermittently evacuated by means of a pumping systemwhich is connected at 11, so as to operate normally at a gas pressure nogreater than a few microns of mercury. The pumping system is not shownin detail, as any known or desired mechanism Afier tank by means of apipe 14.- The for such purpose may be utilized within the spirit lof myinvention.

I have provided a novel glow-discharge mechanism 13 which is connectedto the rectilow discharge device consists of upper and lower electrodes15 and 16, each comprising a base portion 17 and .18 and a flat-toppedcentral nob or projectlon 19 and 20, respectively, the two projectionsextending toward each other and separated by any desired distance suchas an inch or less. For convenience in manufacture, the bottom electrode16 is made in two pieces, the central knob portion 20 being made in theform of a separate plug having a depending projection 21 fitting intothe pipe 14. The two electrodes 15 and 16 are held in spaced relation bya tubular insulating member 23, which may be of glass or porcelain, andwhich surrounds the knobs 19 and 2() with as close a fit as ismechanically feasible, for a purpose to be hereinafter mentioned. Thetubular insulating member 23 is spaced from the base members 17 and 18of the respective electrodes by means of rubber gaskets 24, or othermeans for effecting a vacuum-tight joint, said gaskets being compressedby means of insulated bolts 25. The problem of effecting a goodvacuum-tight joint is very simple because the device always operates atroom temperature.

An electromotive force of the order of 500 to 5000 or more volts isapplied across the electrodes 15 and 16 by means of a step-uptransformer 28 which may be provided with voltage-changingmeans 29 forthe purpose of adjusting the pressure at which the glowdischarge devicebegins to operate. In the embodiment of my invention shown in the'drawings, the step-up transformer 28 is energized from the auxiliary11G-volt alternating-current bus 3() of the rectifier station.

When a glow-discharge device operates under variable conditions ofvoltage, vacuum and electrode-spacing, different break-down voltages areobtained for different voltages, gas pressures and electrode spacings,according to the gaseous ionization in the space between the electrodes.If the vacuum is suiciently high, the electrons, in passing from oneelectrode to the other under the influence of the electrostatic field orapplied voltage, do not encounter enough gas molecules to produce theionization necessary to ization by collision. y

In Fig.2, I have plotted a curve 33 showinitiate the glow discharge. Onthe other hand, if the gas pressure, or number of gas molecules, is `toogreat, the electrons are stopped by collisions with gas molecules beforethe electrons have had an opportunity to attain a velocity necessary toproduce 1oning the relation of the break-down voltage to the airpressure, in a particular gap device having electrodes spaced about oneinch apart, although it will be understood that I am not limited to thespecific values so indicated. It will be noted that, for the highervacua, or low pressures, itl requires relatively high voltages to breakdown the gap. As the pressure increases, the breakdown voltage rapidlyfalls to a minimum break-down voltage which may be of the order of 360volts, and as the air pressure still further increases, the break-downvoltage again rises, but at a more gradual rate.

For gaps which are spaced a. greater distance than that corresponding tothe curve 33, or for points along the sides of the electrodes which arespaced a. greater distance apart, the ga breaks down at lower airpressures, as indicated by the dotted-line curve 34, because of thegreater opportunitiesfor collision which are obtained by reason of thelonger distance which an electron travels in passing from one electrodeto another.' It is noted that the same minimum discharge voltage isobtained with the different spacingV of the electrodes, but that inevery case any given break-down voltage is obtained at a lower airpressure for the more widely separated gap electrodes.

It is for the reason above explained that I have constructed myelectrodes 15 and 16 with e'ective portions 19 and 20 which fit asclosely as possible into the tubular insulating members 23, in order teprevent the break- .ing down of the gap by reason of the variabledischarge distances of electrons attempting to pass from the sides ot'one electrode to the sides of the other.

In like manner,I have provided the central plug near 20 of my lowerelectrode with a slot 37 extending up to a point above the flange orbase member 18 of the lower electrode, as shown in Figs. 1 and 3, inorder to provide a restricted tortuous path connecting the gap spacewith the pipe 14, or, in general, a path within which no electrictieldlexists and so shaped as to collect all ions and electrons, so thatelectrons cannot travel from the upper electrode 19 to points at variousdistances along the inside of the pipe 14.

In order Ato provide an indication of the' break-down of thedischargegap, I have provided an electro-responsive relay 40, which may be acurrent relay or, as shown in the drawing, a watt-responsive relay,

only of the order of which closes a contact 41 in response to the smallamount of energy which is consumed in .the glow-discharge device when aglowdischarge current is passing therethrough.

The relay is preferably placed in the primary circuit of the step-uptransformer 28 because of the largercurrents therein available, thesecondary discharge currents being a few milliamperes at some 5000volts. The relay 40 is also pref- 75 erably of a sluggishly acting typebecause, when the glow discharge device begins to operate, the dischargelick'ers somewhat and it is desirable to prevent the relay from openingand closing a large number of times before it finally moves to itssteady-state position.

The relay Contact 4 1, when closed, is utilized to energize the openingcoil 10 of the main switch 8, to shut down the rectifier in S5 responseto a predetermined rise in the gas pressure within the rectifier tank.

The closing of the contact member 41 also energizes a lock-out relay 42which deenergizes the closing coil 9 of the main switch 8, said closingcoil having a supply conductor 43 which leads to the control equipment(not shown) provided at the sub-station.

In operation, the rectilier may be shut down by the glow-responsiverelay 40 if the 95 pressure increases to any predetermined value such asthat corresponding to a mercury column of 15 or 20 microns.

It will be observed that the particular preferred form ofglow-dischargedevice which I have designed, is made of massive iron parts and amassive tubular insulator member such as the insulators used in therectiier tank itself. It is evident, therefore, that I haveI provided avacuum-measuring device 13 which is no more susceptible to breakage orinjury than the anode holders oi the rectifier itself.

While I have shown my glow-discharge device as being located on a pipewhich bends out from the tank, it will be understood that suchillustration is only for convenience in showing the apparatus in assingle ligure. In an actual rectifier tank, the glow-discharge device islocated above the top plate of the tank, either between two of theanodes or within the circle of the anodes of the tank. v

It will be noted from. Fig. 2, that with nearly 5000 volts electricalpressure applied to the electrodes, my glow-discharge device will breakdown when the air pressure rises initiated, becomes higher than theapplied discharge is discontinued.

If a rectifier is shut down by the operay tion of m relay 40, inresponse to poor vacuum con itions such las may be caused by a leak, itmay be that during theinterval in which lthe cause of shut-down is beinginvestigated by the attendants of the plant, the pressure may increasebeyond the point 45, so that the relay 40 opens and either automaticallystarts the tank again or at least permits the tank to be started in casean attempt should be made thereafter to restart the rectifier.

In the actual installation, as I have designed it, the operation of therelay 4()l is utilized to trip out the trip coil of a master controllersuch that the plant cannot be a ain started without manual manipulation,ifg the vacuum is so poor as to cause the operation o the said relay 40,and it is expected that no operator will attempt to restart therectifier without assuring himself as to the proper vacuum conditions.

However, to make the device absolutely fool-proof, it is possible to addan attachment which is responsive to pressures of the order of one-halfmillimeter ora millimeter of mercury, in order to operate at a point, asindicated at 46 in Fig. 2, while the glowdischarge device is stillvfunctioning and before the glow is interrupted by an increase inpressure beyond the point in Fig. 2. Such a device may be a simplemanometer or mercury switch, as indicated at 47 in Fig. 1,

in which a mercury column 48 spills over and makes contact with a secondmercury1 column 49 in response to excessive increases in the gaspressure to be measured. By this means, a circuit 50 is established tothe lockout relay 42 hereinabove described.

lVhile I have described a form of glowdischarge device 13 substantiallyas I have constructed it in actual practice, it may be found that itwill have more constant operating characteristics by being constructedon the point-to-cylinder discharge principle, as indicated by way ofexample, in Fig. 4, wherein a cup-like metal electrode is providedinstead of the solid electrode 20 of Fig. 1, the other electrode beingan axially depending wire 61 which is tightly enclosed by an insulatingsleeve 62, except for the extreme tip 63 ot the wire, which is exposed.A tip 64 of carbon or graphite is preferably pushed over the wire tip 63in orderto'preserve its life. The glow-discharge space is connected tothe pipe 14a by a tortuous path 37 It will be understood that theconstruction, in Fig. 4, is otherwise similar to that shown in Fig. 1.

In operation, the glow-discharge device of Fig. 4 provides a very sharpbreakdownv at, or near, the surface of the point or small electrode 64.By reason of the highly concentrated field in the region of the pointelectrode, the device may be found to be much more sensitive to changesin pressure than a device in'whioh the field is uniform, although thelatterv device has proved to be successful in operation. A peculiarityof the operation of the point-discharge device, which may, in somerespects, be considered disadvantagcous, is that it is a rectif ingdevice and hence, unless two oppositely conducting devices are utilized,re uires a somewhat more slowly acting, an hence more expensive, relaythan the non-rectifying glow-discharge device 13 of Fig. 1, 1n order toprevent chattering upon the occurrence of a discharge.

While I have speciiically described and explained my invention inrelation to a particular form of embodiment, I desire to be understoodthat such particular description and explanation is only suggestive andnot intended by way of limitation. It is desired, therefore, that theappended claims shall be accorded the broadest interpretation consistentwith their language and the prior art.

I claim as my invention:

1. A vacuum-responsive mechanism comprising a glow-discharge devicehaving spaced electrodes operating in the vacuum in question, a sourceof electromotive force higher than the minimum glow-discharge breakdownvoltage applied to said electrodes, the applied electromotive force andthe electrode spacing being such that no glow discharge can take placeduring normal vacuum conditions, and electrical-energy responsive meansfor operating in response to the flow of a glow-discharge current insaid glow-discharge device.

2. The combination with a vessel n ormally having a vacuum correspondingto a gas pressure no greater than a few microns of mercury, of amechanism associated therewith and responsive to a predetermined increase in the gas pressure therein, said mechanism comprising aglow-discharge device having spaced electrodes operating in the vacuumin question, a source of electromotive force higher than about 360 voltsapplied to said electrodes, the ap lied electromotive force and theelectro e spacing being such that no glow discharge can take placeduring normal vacuum conditions, and electrical-energy responsive meansfor operating in response to the flow of a glowdischarge current in saidglow-discharge device.

3. The combination with a vessel normally having a vacuum correspondingto a gas pressure no greaterthan a few microns of mercury, of amechanism associated therewith and responsive to a predeterminedincrease in the gas pressure therein, said mechanism comprising aglow-discharge device having spaced electrodes operating in the vacuumin question, a source of electromo-` tive force higher than about 360volts applied to said electrodes, the applied electromotive force andthe electrode spacing being such that no glow discharge can take lplaceduring normal vacuum conditions, electrical-energy responsive means foroperating in response to the flow of a glow-discharge current in saidglow-discharge device, and additional means operating in response tostill further increases in the gas pressure and before theglow-discharge device ceases to member,

discharge as a result of said pressure.

4. A vacuum-responsive mechanism adapted to operate in response to anincrease in gas pressure above values corresponding to a relatively goodvacuum, said mechanism being characterized by having two electrodes, atubular insulating member separating said electrodes, a vacuum-tightjoint between each electrode and said insulating and a pipe connected tothe discharge gapv through a path within which substantially no electricfield exists, said path being tortuously shaped whereby it will collectall ions and electrons.

5. A vacuum-responsive mechanism adaptincreased gas i ed to operate inresponse to a change in gas pressure, said mechanism being characterizedby having two electrodes, each having a base portion and a fiat-toppedcentral knob or projection extending toward the other electrode, atubular insulating member separating the base portions of saidelectrodes and closely surrounding said knobs, a vacuum-tight jointbetween each electrode and said insulating member, and a pipe connectedto the discharge gap through a restricted, tortuous path.

, 6. A vacuum-responsive mechanism 'comrprising a glow-dischargedevicehavingr spaced electrodes operating in the vacuum a source ofelectromotive force' about 360 volts appliedto said slow acting'electrical relay for f 1n question, higher than electrodes, a operatingin response to the How of a glowdischarge current in said glow-dischargedevice, and apparatus arranged and adapted to be controlled in responseto said relay.

A vacuum-responsive mechanism comprising a glow-discharge device havingelectrodes operating in the vacuum in question,

- a sourceof electromotive force higher than about 360 voltsl applied tosaid electrodes, a sluggishly responsive electrical relay for operatingin response to the iow of a glowdischarge current in saidglow-discharge'device, means for varying the electromotive force of thesaid source, and apparatus arranged and adapted to be controlledinresponse to said relay.

8. The method of utilizing a glow-discharge device which is connected toa highly evacuated vessel for the purpose of securing anfindication ofpoor vacuum in said vessel which comprises the application to saidglow-discharge device of a voltage which is just sufficient to causebreak-down'of the glow-discharge device at the poorest permissiblevacuum in said vessel, and obtaining an indication of the occurrence ofany glow discharge which takes place in case the vacuum' becomes poorerthan said predetermined amount.

In testimony whereof, I have hereunto subscribed my naine this 3rd dayof Au` gust, 1927. i

LLOYD SMEDE.

